The present invention relates to a method for forming and thermosealing one end of a packaging container comprising layers of thermosealable material, the packaging container being displaced by means of a conveyor through a forming station and a sealing station.
The present invention also relates to an apparatus for forming and thermosealing one end of a packaging container which is displaced by means of a conveyor through a forming station and a sealing station.
Consumer packages for liquid contents such as milk or juice have long been known in the art and occur in numerous different types and sizes. The packaging containers are normally manufactured from a laminated material which comprises layers of fibrous material, e.g. paper, as well as layers of thermoplastic which not only render the packaging laminate liquid-tight but also make for thermosealing thereof. The laminate may also include additional layers, for example layers of gas barrier material such as aluminium foil (Alifoil) for further improving the properties of the laminate in protecting and keeping the product packed in the packaging container in pristine condition.
In a common type of packing and filling machine which is described in European Patent 217.282, a semi-manufacture is utilised in the form of tubular, flat-laid packaging container blanks. The blanks are provided in a per se known manner with a longitudinal seal as well as a pattern of crease lines in order to make for reforming of both ends of the blank into an end portion (top and bottom portion, respectively). Normally, the prefabricated, flat-laid blank is raised so that it obtains a square or rectangular cross-sectional configuration, whereafter it is provided, by folding and sealing of end wall panels located at the one end of the blank and defined by means of crease lines, with a liquid-tight bottom. With the aid of a conveyor, the blank provided with a bottom is thereafter displaced to a filling station in which it is supplied with the desired quantity of suitable contents, e.g. milk. After completed filling, the thus filled blank is displaced an additional step to a subsequent sealing station in which the upper end of the blank (after possible additional forming) is sealed together in a liquid-tight transverse seal. In the forming operation, triangular corner flaps occur for reasons of geometry, and the flaps may be folded outwards or inwards and fixed in place in a suitable manner.
The above-described procedure takes place in conventional machines, normally as an intermittent process, i.e. the conveyor stepwise displaces the different packaging containers between the stations for bottom forming/sealing, filling and top forming/sealing. Since each packaging container, in the instant of processing, is located in a stationary, accurately fixed position, processing and sealing may take place with the aid of intermittently operating, reciprocating processing tools. Normally, conventional sealing jaws are employed in this connection for thermosealing, the jaws reciprocating in a direction substantially transversely in relation to the direction of movement of the conveyor. In certain types of machines, preforming of the ends of the packaging container blank takes place partly during the movement of the conveyor up to the sealing stations, e.g. with the aid of rotary or fixed forming devices. For example, use is occasionally made of guides converging seen in the direction of movement of the conveyor in order to urge the end wall panels subsequently forming the end wall of the blank in a direction towards one another as a preparatory step to the actual final forming and sealing.
The striving to produce packing or filling machines operating at high output capacity has entailed increasingly faster conveyor speeds and shorter stay-times in the different processing stations. However, in stepwise advancement of the conveyor, a limit is soon reached at which the contents, in particular if they are of low viscosity such as, for example, milk or juice, begin to slosh out of the packaging containers in connection with the jerking stepwise advancement movement. Attempts to adapt the acceleration and retardation speeds of the conveyor to meet the viscosity of the contents have entailed certain improvements, but in order to ensure a further increased machine capacity, it is necessary to depart from the intermittent conveyor movement and provide the machine with a continuously operating conveyor running at constant speed. This in turn renders impossible the employment of stationary processing tools which reciprocate transversely in relation to the conveyor. As a result, there is a general need in the art to realise a method of forming and thermosealing packaging containers in continuously moving containers, regardless of whether these are moved at varying or constant speed.
One object of the present invention is to realise a method of forming and thermosealing one end of a packaging container while the packaging container is fed, without stopping, through a processing station, e.g. a station for forming or sealing of the end portion of the packaging container.
A further object of the present invention is to realise a method of forming and thermosealing one end of a packaging container, the method being suitable for use in continuous advancement of packaging containers in relation to fixed processing stations.
Yet a further object of the present invention is to realise a method of forming and thermosealing one end of a packaging container, the method making for considerably increased production speed as compared with prior art methods.
Still a further object of the present invention is finally to realise a method of forming and thermosealing one end of a packaging container, the method not suffering from the limitations and drawbacks inherent in prior art, similar methods.
These and other objects have been attained according to the present invention in that the method described by way of introduction has been given the characterizing features that the conveyor displaces the packaging container through the forming station in contact with mechanical forming devices which progressively reform the packaging container end until such time as opposing walls thereof meet one another in a sealing fin oriented in the direction of movement of the packaging container, whereafter the conveyor further displaces the packaging container end in between sealing devices disposed in the sealing station which heat thermoplastic material located in the sealing fin to sealing temperature, whereafter wall portions included in the sealing fin are mechanically urged against one another during simultaneous cooling and continued advancement.
There is also a need in the art to realise a machine for the continuous part production of packaging containers in accordance with the above-disclosed method, i.e. a machine in which a continuously running conveyor displaces packaging containers through sequentially disposed processing stations, e.g. stations for forming and thermosealing of an end portion of a packaging container.
One object of the present invention is to realise an apparatus for forming and thermosealing one end of a packaging container which continuously moves through stations for forming and sealing.
A further object of the present invention is to realise an apparatus for forming and thermosealing one end of a packaging container, the apparatus making it possible to process continuously moving packaging container blanks, i.e. packaging container blanks advanced by means of a conveyor.
Yet a further object of the present invention is to realise an apparatus for forming and thermosealing one end of a packaging container, the apparatus including stationary forming and sealing devices.
Still a further object of the present invention is to realise an apparatus for forming and thermosealing one end of a packaging container, the apparatus lacking intermittently moving parts.
Yet a further object of the present invention is finally to realise an apparatus for forming and thermosealing one end of a packaging container, the apparatusxe2x80x94despite simple and economical design and constructionxe2x80x94making for a packaging or filling machine with considerably increased capacity compared with prior art, intermittently operating machines.
The above and other objects have been attained according to the present invention in that an apparatus of the type described by way of introduction has been given the characterizing features that the forming station includes a mechanical forming device which is disposed along the conveyor a distance therefrom, as well as sealing devices disposed in the sealing station, the sealing devices similarly extending along the conveyor a distance therefrom and being disposed to heat a sealing region of the packaging container, and also compression devices disposed after the sealing devices and disposed to mechanically compress the heated wall portions so that these, after cooling, are sealed to one another in liquid-tight fashion.
The method and the apparatus according to the present invention thus make possible, through their continuous operational mode, a packing and filling machine with a continuously running packaging conveyor, which entails not only a considerably higher output capacity but also smoother operation and reduced wear compared with packing and filling machines of prior art type in which both the packaging conveyor and the processing tools move intermittently.